The invention relates to a seat cleaning-capable double-seat valve with two serially arranged closing elements, moveable relative to each other and designed as slide pistons, which prevent in the closed position of the double-seat valve the overflow of fluids from one valve housing part into another through a connecting opening connecting the valve housing parts with each other and which border both in the closed and open position a leakage cavity, which is connected with the surroundings of the double-seat valve via a tubular shaft arranged on the low-lying (in relation to a vertical normal position of the double-seat valve), second closing element, in which a drainage hole is arranged. The second, independently driven closing element is thereby designed larger than the first, independently driven closing element so that, as a result, the double-seat valve opens downward and the drainage of the leakage cavity also takes place downward. The closing elements are actuated via valve rods, both of which are led upward out of a valve housing and into a drive.
A so-called leakage-free switching double-valve arrangement, which has important characteristics of the initially described seat cleaning-capable double-seat valve, is known from EP 0 646 741 A1. This known double-seat valve has two closing elements designed as slide pistons. It opens, in relation to a vertical normal position, downward and the drainage of the leakage cavity also takes place downward, and namely via a tubular shaft formed on the lower-lying closing element, in which a drainage hole is arranged and which is led downward out of the valve housing. The two closing elements are each transferable to a rinse position independently of each other through a partial lift arranged opposite the opening movement, in which the respective closing element is free of its valve seating and is adjacent to a housing stop provided with rinsing agent passages. The rinsing agent passages thereby restrict the cleaning agent quantity during the respective seat cleaning. The closing elements are actuated via valve rods, which both lead upward out of a valve housing and into a drive. In order to enable the removability of the overhead, smaller and the low-lying, larger closing element in one upwards movement, the valve seats are provided with sealing rings, which are held by housing inserts. These housing inserts are inserted into the valve housing from the side lying opposite the tubular shaft.
In the case of the known double-seat valve according to EP 0 646 741 A1, it is advantageous, like with all other double-seat valves that open downward and have a leakage drain led downward out of the valve housing, that in the open position of the double-seat valve the passage cross-section of a connecting opening connecting the two valve housing parts is not constricted by the cross-section of the leakage drain. This then reduces in particular the nominal width of the valve housing determined by the passage cross-section of the connecting opening by one to two nominal widths when, as required in the USA, the passage cross-section of the leakage drain between the leakage cavity and the surroundings of the double-seat valve must be the same as the largest passage cross-section of the pipeline connected to the double-seat valve.
In the case of the known double-seat valve according to EP 0 646 741 A1, it is disadvantageous that it is at best leakage-resistant and not, as the title claims, leakage-free. The switch leakage results from the fact that in the case of each opening or closing lift in the space, which is bordered on the valve housing side on one side between the two seat seals and on the closing element side on the other side, liquid is locked in and that this liquid gets into the leakage cavity and from there into the leakage drain after separation of the two closing elements on the center seal operating between both. It is also disadvantageous that the respective seat cleaning flow, which makes its way through the rinsing agent passages at the associated housing stop and is primarily oriented axially/radially, pressurizes in a more or less uncontrolled and turbulent manner the seat seal located in the closed position.
With the known double-seat valve according to EP 0 646 741 A1, the cleaning agent quantity during the respective seat cleaning can be limited, as desired. The requirements set in certain countries for such a double-seat valve are however more comprehensive. For example, it is required in the USA that no cleaning agent can pass through in the case of larger seal defects or even the failure of one of the two seat seals in the course of the seat cleaning of the other closing element. Under these conditions, it is not only required of these types of double-seat valves that they restrict the cleaning agent quantity and avoid a direct pressurization of the seat areas during the seat cleaning, but also that they remove the seat cleaning flow in the most turbulence-free manner possible first in the leakage cavity and from there into the surroundings without the respectively closed seat area being directly impacted by this seat cleaning flow or being pressurized such that pressure is increased.
Direct impact is understood to be every speed component of the respective seat cleaning flow, directed orthogonally onto the walls delimiting the seat. It has been shown that any such direct impact leads to a conversion of the kinetic flow energy into static pressure. Depending on the angle of impact of the flow against the wall or body surface, a branching of the flow results in a so-called “branching flow line”, wherein the latter divides the flow into two halves. The branching flow line itself runs up against the so-called “stagnation point”, such that the speed at this location is zero. The pressure increase as a result of this stoppage of the speed is also called “dynamic pressure”. The mechanisms increasing the pressure, described above, generate a leakage flow across the respective gap between the closing element in the assigned seat, and the seat seal that is defective or no longer present at all. Therefore, a direct impact of the seat cleaning flow on the surface delimiting the leakage cavity is always counterproductive.
A double-seat valve opening upward, in relation to a vertical normal position, which allows a cleaning of the respective released seat due to its function, also called a seat cleaning-capable double-seat valve, is known from DE 196 08 792 C2. In the case of this double-seat valve, the cleaning agent quantity for the respective seat cleaning can be controlled by so-called choke gaps and measured very closely. Moreover, a direct pressurization of the respectively closed seat in the course of the seat cleaning of the other seat is prevented through guidance and steering of the seat cleaning flows.
The seat cleaning-capable double-seat valve according to DE 196 08 792 C2 has two so-called seat cleaning positions, wherein the first seat cleaning position is generated by a first partial lift directed opposite the opening lift. In this position, the cylindrical appendage arranged on the leakage-space-side on the first closing element with the associated cylindrical first seat forms a so-called choke gap, via which the cleaning agent quantity led out of the neighboring first valve housing part can be restricted. The seat cleaning position of the second closing element takes place through a second partial lift arranged similarly with respect to the opening lift, wherein in the partially open position the cylindrical appendage arranged on the leakage cavity side on the second closing element with the associated part of the connecting opening forms a second choke gap, which limits the quantity of the second seat cleaning flow generated in this seat cleaning position.
Since the two closing elements and the associated cylindrical appendages have different diameters, the respectively associated sections of the connecting opening are also different in diameter so that a transition surface materializes between these two diameters. In the case of the seat cleaning position of the first closing element, the first seat cleaning flow flows along the cylindrical seat and hits the front-side boundary at the second closing element, wherein at least a direct impact of the first seat cleaning flow on the second choke gap and thus the seat area of the second closing element is prevented by the diameter difference between the two sections of the connecting opening. In the case of the seat cleaning position of the second closing element, the second seat cleaning flow is deflected radially inward at the transition surface bridging the diameter difference between the sections of the connecting opening and bypasses the upper frontal periphery of the first closing element. Also in this case, an indirect impact of the second seat cleaning flow on the first choke gap and thus the seat area of the first closing element is thereby prevented.
A seat cleaning-capable double-seat valve, which is improved with respect to the state of the art described above among other things in that the most turbulence-free discharge of the seat-cleaning flow into and out of the leakage cavity is ensured and a pressure-increasing direct pressurization of the seat area is securely avoided, is known from WO 2007/054131 A1. This is achieved among other things through a transition surface between the two seats of the closing elements and an annular recess in the shape of a special deflection surface in the dependently driven, larger closing element. A center seal is arranged between the two closing elements so that this closing element configuration in the strict sense of the word is more of a leakage-resistant than a leakage-free switching.
A seat cleaning-capable double-seat valve, which is improved with respect to the state of the art described above according to WO 2007/054131 A1 through mainly leakage-free switching, is also known from WO 2007/054134 A1. This is achieved in that the dependently driven, larger closing element has a recess with a mainly cylindrical circumferential wall flush with the seat of the smaller closing element on the end facing the independently driven, smaller closing element, and the recess is dimensioned to receive in a sealing manner an end section and a radial seal of the smaller closing element during the opening movement before the larger closing element opens.
The object of the present invention is to achieve a leakage-free switching in a seat cleaning-capable, downward-opening double-seat valve and to avoid a pressure-increasing direct pressurization of the closed seat area during the respective seat cleaning as well as to ensure the most turbulence-free possible discharge of the seat cleaning flow into and out of the leakage cavity.